Roasting of zinc sulphide ores preparatory to leaching



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HERBERT WILLIAM GEPP, OF MELBOURNE, VICTORIA, -AUSTRALIA.

I ROASTING OF ZINC SULPHIDE GEES PREPARATORY T0 LEACHING.

No Drawing.

To all who/nit may concern:

Be it known that I, HERBERT \VILLIAM GEPP, of Collins House, 360 Collins Street,

Melbourne, in the State of Yictoria, Cornmonwealth of Australia, have invented cer-.

atory to leaching with sulphuric acid or spent electrolyte for the formation of zinc sulphate solution prior to electrolysis tor the deposition of metallic zinc or spelter.

The invention is applicable to any process which involves the preparation of solutions of zinc sulphate such as the manufacture of lithopone and such like processes.

This invention relates to the treatment of concentrates, slimes, tailings and other metallurgical products as well as to crude ores and it will be understood that in this specification the term ores will include metalliferous products as well as the crude material.

The methods which have become standard for the roasting of zinc sulphide ores for the distillation process have been found to be more or less satisfactory when the roasted ore is to be leached with sulphuric acid.

.In the roasting of ores preparatory to distillation it is sought to eliminate the sulpilinr whether present as sulphide or sulp ate.

On the other hand when the ores are. to he leached with sulphuric acid the presence'of sulphates is an advantage, as it reduces the amount of sulphuric acid from an outside source which has to be added. This, of course, is true, more or less, in the electrolytic process, and still more so in the manufacture of lithopone where practically-the whole of the sulphuric acid appears in the final product as barium sulphate.

In the electrolytic zinc process it is usually necessary to add a quantity of sulphuric acid to the leaching solution in order to make up losses occasioned in the working of the process and to maintain the proper concentratipn of zinc in the solution.

Application filed August 8, 1921.

Serial No. 490,711.

In the roasting of zinc suphide ores, when it is desired to effect the more or less com plete elimination, of -the sulphur and to obtain a -dead roast or sweet roast (such as is, the practice preparatory to the distillation process) ithas been found necessary to maintain the operation at a high temperature and if the gases are to be used for the manufactureof sulphuric acid the admission of air must be carefully controlled;

In the roasting of zinc sulphide ores.

when it is desired to ellect a sulphating roast and to obtain a maximum proportion of metallic sulphates, it .is necessary to maintain the temperature as low as possible to prevent the breaking up of the metallic sulphates formed (and in particular zinc sulphate) and further an excess of air is required to effect the oxidation 'to sulphates which renders the gases. too dilute for the manufacture of sulphuric acid.

The object of this invention is to provide certain improvements in the roasting of zinc sulphide ores preparatory to leaching whereby a-sulphating roast is effected with the formation of a maximum quantity of metallic sulphates which when introduced into the leaching solution reduces the amountof sulphuric acid which would otherwise be required to be added thereto or obviates such additions altogether.

I accomplish this object by first roasting the ores to a dead roast, then mixing the same with suflicient sulphide sulphur bearing material to bring the sulphide sulphur contents of the mixture to about 2% then roasting the said mixture at a low temperature and in the presence of an excess of air under such conditions that the sulphide sulphur is converted to sulphate then at intervals adding further quantities of sulphide sulphur bearing material and again roasting under such conditions that the additional sulphide sulphur is converted to sulphate whereby a maximum proportion of metallic sulphates is formed.

It will be obvious that where the ore does not requireto be dead roasted or sweet roasted or hasv been previously approximately dead roasted the 2% mixture is subjected to the second operation which consists more particularly in roasting the 2% mixture at a relatively low temperature in the presence of an excess of air to convert the said mixture to a sulphate and at intervals adding further quantities of green or unroasted sulphide ores'to keep the mixture at approximately 2% sulphide sulphur content continuing the roast under such conditions that the additional sulphide sulphur is converted into sulphate .whereby a maximum proportion of metallic sulphate is formed.

In carrying this invention into effect when treating zinc blende ores, the ore is first subjected to a dead or sweet roast at a high temperature whereby the sulphide sulphur contents is reduced to aminimum. To this dead roast material is added sulphide sulphur preferably in the form of green or unroasted concentrates bringing the sulphide sulphur contents of the mixture to approximately. 2%. This mixture isthen fed into the furnace and is roasted at a relatively low temperature in the presence of an excess of air. As the sulphide sulphur contents of the mixture is sulphatecl further additions of sulphide sulphur are made at requisite intervals so as to preferably bring the sulphide sulphur contents up to approximately 2%; continuing the roast under such conditions that the sulphide sulphur is converted into sulphate and whereby the maximum proportion of metallic sulphates is formed.

Where roasted calcine is delivered to the reduction works with the sulphide sulphur reduced to a minimumand also when treating oxidized ores, it is necessary to add sulphide sulphur preferably in the form of green or unroasted concentrates during the sulphating operation. As the efliciency of the sulphate formation increases as'the percentage of sulphide sulphur decreases, it is preferable to add the green sulphide conto approximately-2% at each addition and then roasting at a low temperature and in the presence of an excess of air under such conditions that a maximum amount of metallic sulfates are formed.'

2. A process for the roasting of zinc sulphide ores which consists infirst roasting the ores to a dead roast then mixing the same with suflicient sulphide sulphur bearing material to bring the sul hide sulphur.

contents of the mixture to a out 2% then roasting the said mixture at a low temperature and in the presence of an excess of air under such conditions that the sulphide sulphur is converted to sulphate then adding further similar quantities of sulphide sulphur bearing material and again roast ing under such conditions that the additional sulphidesulphur is converted to sulphate whereby a maximum proportion of metallic.

sulphates is formed substantially as described.

In testimony whereof I afi'ix my signature.

HERBERT WILLIAM GEPP. Witnesses:

M. SUMMERLEIGH, G. R. CULLEN. 

